[asan] Fix unsupported test on Android

Summary:
`pvalloc` appears to not be available on Android. Mark the failing test as
unsupported on that platform.

Reviewers: alekseyshl, vitalybuka

Reviewed By: alekseyshl, vitalybuka

Subscribers: srhines, kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D36339

llvm-svn: 310133